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Assertion: On stimulation, a muscle cell releases calcium ions (Ca2+) from sarcoplasmic reticulum.
Reason: By reacting with a protein complex, Ca2+ uncover active sites on the actin filaments.
  • a)
    If both Assertion and Reason are true and Reason is the correct explanation of Assertion.
  • b)
    If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
  • c)
    If Assertion is true but Reason is false.
  • d)
    If both Assertion and Reason are false.
Correct answer is option 'B'. Can you explain this answer?
Most Upvoted Answer
Assertion: On stimulation, a muscle cell releases calcium ions (Ca2+) ...
A neural signal on reaching the neuromuscular junction releases a neurotransmitter (acetylcholine) which generates an action potential in the sarcolemma. This spreads through the muscle fibre and causes the release of calcium ions from sarcoplasmic reticulum into the sarcoplasm. Increase in Ca2+ level leads to the binding of calcium with a subunit of troponin on actin filaments and thereby, removing the mask of active sites for myosin.
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Assertion: On stimulation, a muscle cell releases calcium ions (Ca2+) ...
Understanding the Assertion and Reason
The assertion and reason provided relate to the physiological process of muscle contraction, primarily focusing on the role of calcium ions.
Assertion Explained
- When a muscle cell is stimulated, it triggers the release of calcium ions (Ca2+) from the sarcoplasmic reticulum.
- This release is crucial as it initiates the contraction process by allowing interaction between myofilaments.
Reason Explained
- Calcium ions bind to troponin, a protein complex associated with the actin filaments.
- This binding causes a conformational change that moves tropomyosin, uncovering the active sites on actin.
- This process allows myosin heads to attach to actin, leading to muscle contraction.
Why Option B is Correct
- Both the assertion and reason are true statements concerning muscle physiology.
- The assertion accurately describes the release of Ca2+ from the sarcoplasmic reticulum upon stimulation.
- The reason correctly identifies the role of Ca2+ in exposing active sites on actin but does not serve as a direct explanation for the assertion of Ca2+ release.
Conclusion
- Therefore, while both components are true, the reason does not directly explain the assertion. Instead, it elaborates on the subsequent role of calcium ions after their release.
- This distinction is crucial for understanding the sequence of events in muscle contraction and is why the correct answer is option 'B'.
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Assertion: On stimulation, a muscle cell releases calcium ions (Ca2+) from sarcoplasmic reticulum.Reason: By reacting with a protein complex, Ca2+ uncover active sites on the actin filaments.a)If both Assertion and Reason are true and Reason is the correct explanation of Assertion.b)If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.c)If Assertion is true but Reason is false.d)If both Assertion and Reason are false.Correct answer is option 'B'. Can you explain this answer?
Question Description
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